Ventilatory control results from the integration of neural information from peripheral and central chemoreceptors by the brain-stem respiratory center. Although attempts have been made to derive the relative contribution of the peripheral and central chemoreceptors under steady-state conditions, little information is available during non- steady-state of ventilatory pertubations. We shall attempt to elucidate these mechanisms under dynamic or changing conditions by measuring breath-by-breath respiratory-rate, tidal volume and minute ventilation using a digital computer for computation and plot-out of the computed variables. Five kinds of CO2 stimuli will be administered: 1) inhalation of CO2 2) transient (20 sec) infusion into ascending aorta and 3) transient elevations of arterial CO2 tension by abruptly increasing cardiac output thereby transiently reducing the overall ventilation to perfusion ratio 4) intra-venous loading of CO2 using a membrane oxygenator 5) providing a "physiological" CO2 stimulus by experimentally redistributing pulmonary blood flow. The above experiments will be repeated following selective denervation of the peripheral chemoreceptors. Plotting the time course of the stimuli (at the known receptor sites) and the tidal volume, breathing frequency and minute ventilation response on a breath-by-breath basis under these conditions should elucidate the role and relative contribution of the peripheral and central chemoreceptors in overall ventilatory control.